Using poultry litter biochars as soil amendments

Abstract

Despite the recent interest in biochars as soil amendments for improving soil quality and increasing soil carbon sequestration, there is inadequate knowledge on the soil amendment properties of these materials produced from different feed stocks and under different pyrolysis conditions. This is particularly true for biochars produced from animal origins. Two biochars produced from poultry litter under different conditions were tested in a pot trial by assessing the yield of radish ('Raphanus sativus' var. Long Scarlet) as well as the soil quality of a hardsetting Chromosol (Alfisol). Four rates of biochar (0, 10, 25, and 50 t/ha), with and without nitrogen application (100 kg N/ha) were investigated. Both biochars, without N fertiliser, produced similar increases in dry matter yield of radish, which were detectable at the lowest application rate, 10 t/ha. The yield increase (%), compared with the unamended control rose from 42% at 10 t/ha to 96% at 50 t/han of biochar application. The yield increases can be attributed largely to the ability of these biochars to increase N availability. Significant additional yield increases, in excess of that due to N fertiliser alone, were observed when N fertiliser was applied together with the biochars, highlighting the other beneficial effects of these biochars. In this regard, the non activated poultry litter biochar produced at lower temperature (450°C) was more effective than the activated biochar produced at higher temperature (550°C), probably due to higher available P content. Biochar addition to the hardsetting soil resulted in significant but different changes in soil chemical and physical properties, including increases in C, N, pH, and available P, but reduction in soil strength. These different effects of the 2 different biochars can be related to their different characteristics. Significantly different changes in soil biology in terms of microbial biomass and earthworm preference properties were also observed between the 2 biochars, but the underlying mechanisms require further research. Our research highlights the importance of feedstock and process conditions during pyrolysis on the properties and, hence, soil amendment values of biochars.